1. Field of the Invention
The present invention relates to a system for drying wood, and more particularly to a thermal dry stem for drying green wood, green bamboo and other green plants (which have been harvested) to produce, in short periods of time, dried wood, dried bamboo and other dried plants which have been stabilized in their water content.
2. Description of the Prior Art
After harvest, green wood (and the like) are rich in water content, and usually carry many insects and their eggs. Consequently, in producing lumbers for building use and/or furniture use, it is usual to dry the green wood and chemically treat the same to kill the insects and their eggs.
In drying process, the green wood is hitherto subjected to natural seasoning in which it is necessary to leave the green wood as it is for a long period of time, for example, three to five years in a wood yard. During this long period of time, it is necessary for workers of the wood yard to frequently move the wood to enhance the drying process thereof. However, leaving the wood for such long period of time in the wood yard results in a poor investment, and is further disadvantageous in preventing the woods from being attached by insect.
Under such circumstances, hitherto, various quick drying processes for drying wood in short periods of time have been proposed. For example, one of these conventional drying processes is of a vacuum drying type. Another of these conventional drying processes is of a thermal heating type using a drying room to which hot air is supplied.
However, dried wood produced by conventional quick drying processes suffer disadvantages in that the wood is not prevented from cracking; and absorbing moisture which causes distortion of the woods, as in the case of dried wood produced by natural seasoning.
In order to solve the above problems inherent in conventional quick drying processes, another conventional process (i.e., a conventional thermal heating type process) has been proposed. In the conventional thermal heating type process, green wood is first housed in a drying room in which a hot combustion gas produced by burning waste wood and the like is introduced so that the green wood is brought into contact with the hot combustion gas so as to be dried and disinfected with heat and various smoke elements of the combustion gas to kill insects and their eggs in the woods, without being subjected to any chemical treatment, and without causing any distortion of the dried wood.
For example, Japanese Patent Laid-Open Nos. Sho 59-129373 and 60-103281 disclose a conventional thermal heating type process in which green wood is housed in a treatment chamber which has: its upper area subjected to a hot blast; and its lower area subjected to a cool blast, so as to dry the wood. These Japanese Patent Laid-Open documents also disclose a system for carrying out a process which is; however, poor in treatment efficiency of the woods. In this process, when large quantity of green wood is housed in the treatment chamber in order to improve the treatment efficiency, the dried wood obtained through the process tend to vary in water content, which makes it impossible to stabilize the products (or dried wood) in quality.